The use of communication cables which include a plurality of optical fibers is rapidly expanding. An optical fiber cable may comprise a plurality of optical glass fibers each of which is protected by at least one layer of a coating material. The optical fibers may be assembled into units in which the fibers are held together by binder ribbons or tubes to provide a core. Another optical fiber cable core includes a ribbon type optical fiber arrangement in which a plurality, such as twelve fibers for example, are arrayed together side by side. A plurality of these ribbons may be stacked to obtain a high fiber count cable. The core is enclosed by a plastic core tube and a plastic jacket. Also, the cable may include metallic strength members or the cable may be all-dielectric.
Whatever the structure of a transmission cable, there must be provisions for splicing transmission media at an end of a given length of cable to corresponding transmission media at an adjacent end of another length of cable. Where two ends of a cable such as a telecommunications cable are spliced together, the splice area is ordinarily housed within a protective arrangement. It is conventional to use a splice closure, within which the transmission media are spliced, wrapped and stored and protected environmentally. Such closures often have included cylindrical covers with one or more longitudinal joints and end plates that surround incoming and outgoing cables and that form seals with the covers. Closures which are effective in providing protection for the splice connections are available in the marketplace, but the assembly of some of these is relatively time consuming, often requiring specialized tools and equipment which in a limited space such as in an underground tunnel or on an overhead pole or line may be difficult to handle and operate.
Optical fiber cables and associated apparatus such as a cable closure, for example, are typically designed and manufactured to avoid problems which may be caused by a variety of anticipated environmental conditions to which the cable and associated apparatus will be exposed. One such condition is the exposure of portions of the cable and the cable closure to water. Potential problems associated with this condition are the entry of water into internal potions of the cable as well as the entry of water into the cable closure in which the cable has been terminated, spliced, stored or branched.
The entry of water into a cable closure is an undesirable condition because water generally has a detrimental effect on the enclosed optical fiber cable, the optical fiber and internal portions of the cable closure. For example, water vapor may attack surface flaws of the external surface of the glass optical fiber and cause stress corrosion. In the presence of water and stress in the optical fiber, a surface flaw in the optical fiber will tend to grow in size. This may result in lower tensile stress fiber breaks. Another detrimental effect from the presence of water in a closure may result if the water freezes. Such a condition may subject the fiber and internal portions of the cable and closure to damaging mechanical loads.
Common to substantially all closures is the requirement that they restrict moisture ingress. In some prior art closures, sealing an optical fiber cable closure to prevent the ingress of water has depended on effecting three different seals. One is a seal formed between a portion of an outer surface of an outer jacket of the cable and a surface of the closure or a surface that is independently sealable with the cable closure. At times it becomes somewhat difficult to match the size and sometimes deformed shape of a cable with flexed seals. A second cable closure seal is a seal associated with a closure cover. The cover portion is caused to seal with, for example, a closure bulkhead portion through which cables extend into the closure. Steps also must be taken, such as by filling interstices in the cable with a water blocking compound or by including a water blocking tape as a sheath component to prevent water that enters interior portions of the cable at a point outside the cable closure from travelling along the length of the cable between adjacent cable sheath components.
In the prior art, it is not uncommon to use a pressurized gas system to prevent the intrusion of moisture. Some systems employ dry air, nitrogen or a similar chemically inert gas in the cables and closures. In this type of reenterable closure, the gas is pressurized to create a flow from enclosed equipment through any openings and prevent the ingress of moisture. In such a system, it is advantageous to minimize the amount of gas leakage to reduce the consumption of pressurized gas and to insure against any requirement of high gas flow to maintain adequate pressure throughout the system. Accordingly, closures and associated equipment should be sealed sufficiently to prevent a reduction in pressure and the loss of gas. At the same time, it is necessary to provide a system which is easily assembled in the field and in which the probability of installer error is relatively low.
Heretofore a number of sealed closure designs have been made available. However, some of these have employed somewhat complicated sealing mechanisms which have added to the cost and which may have required close attention to assemble. Efforts have been made to provide closures which may be assembled more rapidly, which are less craft sensitive and which include fewer parts.
Another commonly used approach of preventing the ingress of water into a closure is to cause the closure to be filled with an encapsulant material. Such a closure may include two sections defined by two bulkheads with cable sealing grommets through which cables extend and a closure cover which is tubular and which has a closed end and an open end. A cable end portion is extended through a first bulkhead into a first chamber and portions of the cable sheath system are removed so that only an end portion of a core tube extends through a second bulkhead into a second chamber. In the just-described closure in which encapsulant materials are used to effect water blocking of the cable sheath system, splice connections are typically located in the second chamber. The blocking of water through portions of the able sheath components into the cable closure occurs in the first chamber. The closure cover is fastened securely and the first chamber is caused to receive a liquid encapsulant material. The encapsulant material is allowed to cure, thus forming a solid potting compound that surrounds the splice connections. The solid, cured potting compound effectively prevents water from entering the cable closure through portions of the cable sheath components.
The just-described cable water blocking arrangement is most practical when access to the interior of the cable closure is not anticipated. Reentry into the closure would most often occur if a new cable were being spliced or connected to another cable within an in-use closure. To effect the introduction of a new cable into the closure, at least a portion of the cured encapsulant material within the closure would have to be removed. The first chamber of the closure is re-potted after a portion of the new cable is introduced to reestablish the closure water blocking capability. The removal of cured encapsulant material and the installation of new encapsulant material is a laborious task. What is needed is a closure which provides at least the same level of protection against water as does an encapsulant, yet is one which presents fewer housekeeping problems.
Notwithstanding the above-enumerated problems, it continues to be necessary to splice together the ends of transmission media such as optical fiber cables in field locations. A new closure is sought after to facilitate splicing in which suitable protection is afforded the optical fibers. Provisions must be included in the sought-after splice closure for holding mechanical splices as well as fusion splices. What is needed and what seemingly is not provided for in the art is a simple system for protecting connective work within a closure from moisture. The sought-after system should be one which allows for relatively easy reentry, which includes few parts, and which is less craft sensitive than prior art closures to stem increasing labor costs.